Traveling crane motor control



March 3, 1953 K. s. KUKA 2,630,554

TRAVELING CRANE MOTOR CONTROL Filed Dec. 23, 1948 Koikob ad swab'gi KuK Q EN-rott Patented Mar. 3, 1953 UNITED STATES PATENT OFFICE TRAVELING CRANE MOTOR CONTROL Kaikobad S. Kuka, J amshedpur, Bihar, India Application December 23, 1948, Serial No. 67,014

3 Claims.

The invention relates generally to systems of control and more particularly to the system of control for direct current motors employed in operating of the long travel mechanism of the electrically operated travelling cranes.

The object of the invention, generally stated, is to provide for controlling the overspeeding as also electromechanical braking of the long travel motion of a travelling crane.

A more specific object of the invention is to prevent overspeeding of a long travel bridge of a crane when the crane is running without any load on the hook, permitting at the same time, the maximum speed when the crane is handling its full load.

A further object of the invention is to provide the standard series type electro-mechanical brake, which drops only when the bridge stops or when the power fails.

For a better understanding of the invention, reference may be made to the following description taken in conjunction with the accompanying drawing, wherein:

The figure is a schematic illustration of a control system wherein the features pertaining to my invention are introduced.

In the drawing an electric motor of the direct current series type is shown provided with an armature A with a series field winding SF, which may be suitably coupled to the operating mechanism of a crane bridge. Since the constructions of the crane bridge long travel mechanism and the manner of installing the motors for operating them, as well as that of mounting of the electro-mechanical brakes are well known, it is not deemed necessary to illustrate these. Notation SB denotes the series type operating coil of the electro-mechanical brake, which is mounted on the motor shaft extension (not shown).

A master switch with a number of cam-operated contacts is provided to control the operation of the motor. The contact segment al of the master switch is disposed to engage the contact finger a which in turn is connected to the line conductor LI. The finger a is also connected over the auxiliary contacts Ma of the line contactor M to give the holding power to the coil MI when the control switch is put on to energize the control panel. Contact segment bl engages the finger b to provide the energizing circuit to the coil TFI of the contactor TF. Contact segment cl engages the finger c for completing the energizing holding circuit for the control when the master switch is moved from its "off position. Contact segment dI engages the finger d for completing the energizing circuit for operating coils IFI and 2Fl of the directional contactors IF and 2F, which when completed effect the closing of contactors IF and 2F. Therefore, when the control switch is closed and the master switch is kept with its operating handle in the ofi position, the main line contactor M is energized and closes its main contacts at M and auxiliary contacts Ma over which the holding circuit for the operating coil MI is obtained.

When the master switch is moved in the direction marked forward X to position I, the contactors IF and 2F are closed and the power circuit for the motor which may be traced from the line conductor LI, over the closed main switch, through the contactor IF, the armature A, the contactor 2F, the series field winding SF, the electro-mechanical brake coil SB resistor R, main line contactor M over the main switch to line L2. The motor is thus caused to operate in one direction called the forward direction and marked X. The resistor R is provided to prevent the excessive starting currents in the motor and also for making it possible to operate the motor at different speeds. In order to short-circuit the sections RI, R2, R3 and R4 of resistor R, the electro-magnetic contactor P, IA, 2A and 3A are provided. P is called the plugging contactor and IA, 2A and 3A are called the accelerating contactors, when the master switch is moved through difierent indicated forward positions 2, 3, 4 and 5, the contact fingers c, d, g, h, z and engage the contact segments cl, dl, fl, gl, hl, El and 5i I in the order named, completing the energizing circuits for the contactor coils IF, 2F, P, IA, 2A and 3A in sequence, which contactors in closing, short-circuit the respective resistor steps and accelerate the motor.

In order, however, to allow the motor to accelerate smoothly without heavy current kicks, the accelerating contactors IA, 2A and 3A are controlled by the relay IAR, ZAR and 3AR. which are called accelerating magnetic time relays. The actuating coil IARI of the relay IAR is connected across the resistor RI, that of ZARI across the resistors RI and R2 in series connection, and that of 3ARI across the resistors RI, R2 and R3 in series connection. These relays are actuated by the voltage drops across the resistor steps to which they are connected. As soon as the motor takes its starting current, the relays IAR, ZAR and 3AR are actuated, pulling in their armatures. Each relay has a set of normally closed contacts which open out as soon as the relays are energized.

Another relay marked PFR is connected across the motor armature over the auxiliary contacts lFa of the contactor IF and over control resistance rsl to the point T3 of the resistor step R2. This relay PFR is designed to be actuated by the combined voltage drops across the armature and the resistor RI and R2. When the relay coil PFRI of the plugging relay for forward and reverse directions, is actuated, its normally open contacts PFR close-and giVe the actuating power to the contactor coil Pl over the finger g and segment Q! of the master switch.

When the master switch is in position 2, contactor coil Pi is energized over the contact PFR of the said plugging relay which pulls in as soon as the motor is connected tothe line. When the contactor P closes, the resistance step R! is short ed. This short-circuits the coil of the relay IAR.

This relay being a time delay relay, it takes time to open out. As soon as the relay IAR drops out, its contacts GAR close, giving circuit to the accelcrating contactor coil IAI, allowing the contactor' l-A to close in its sequence. The contactor IA in turn short-circuits the resistor R2 and the coil 2ARl of the its relay which then opens out and closes its contacts to allow 2A contactor to go in, which in turn de-energizes the coil 3ARI of its relay which allows the contactor 3A to be pulled in. Thus when the master switch is moved fast to position 5' in forward direction, the motor is accelerated smoothly in a fixed time sequence, independent of the speed of moving themaster switch handle.

When it is desired to move the crane in the opposite direction, i. e., in the reverse direction XI, the master switch is moved in direction indicated reverse, when the control segments el, j2,lg2, M, 2 and i2 engage the fingers e, f, g, h, i, and 7" in sequence. In the position i of reverse direction, the contactors IR and 2B get energized which connects the armature A in the reversed polarity, allowin the motor to move in the opposite direction. The control of the contactors P, IA, 2A and 3A is however exactly the same asin the forward position of the master switch.

If, however, itis desired tobring the motion to a dead stop when the motor is moving in one direction, say forward, the master switch handle is: brought suddenly to the reverse direction. The motor armature gets disconnected from its forward direction by dropping out of the contactors EF and 2E, and is at once connected to reverse direction by the energizing of the contactors l-R' and 2R. The motor is thus electrically connected torotate in the opposite direction, whereas due to the momentum of the crane the armature is still kept rotating in the initial forward direction. The motor thus auto1natically generates abraking action which slows down the bridge motion. The process of stopping the motor by reversing its armature connections is technically known as electrical plugging. During the plugging period, the voltage across the relay coil PFRI is almost zero. The relay thus drops out, opening its contacts, which opens the energizing circuit to the contactors P, IA, 2A and 3A, allowing the whole resistance R to remain in the circuit to limit the current through the motor.

The above describes in general the operation of a standard reversing lugging magnetic controller as normally used on crane service.

When direct current series-wound motors are used on crane service, the ultimate speed depends on the actual load on the motor. The characteristics of the series-wound motor is such that its speed increases as the load on the motor is reduced. Thus if a motor is selected on the basis of starting torque and the mechanism is geared on the basis of a certain definite speed on full load, it is clear that the ultimate speed increases as the load is reduced, and in case of a crane with no load on the hook, th ultimate speed becomes sometimes as high as 200% of the full load speed. When therefore the motion is to be arrested from that high speed, the shocks on the crane as well as the building are increased manifold because the shocks vary as the square of the speed. The adverse effects of these shocks on the buildings can therefore be reduced if it ispossible to prevent the overspeedin of the motor at light loads.

To arrest the speed of the crane in an emer gency when electrical power suddenly fails, a mechanical. brake is absolutely necessary. To that end, it is possible to provide a mechanically operated foot brake, or an electro-mechanical brake, or an electro-hydraulic brake. The mechanically operated foot brakes were first tried and rejected as they depend on the operator and give a good deal of trouble due to long. leverage. They were then discarded in favour of electromechanical brake. The series type electro-mechanical brake, though the simplest in operation, has not been generally adopted for long travel motion, because in actual service, itsuddenly sets-in whenever the master switch handle is moved through the oif position to change the direction of motion. This creates a suddenv jerk on the crane, causing swinging of the load hanging on the hook creating difiiculties in load spotting- It has therefore not been used in practice.

The shunt-type electro-mechanical' brake is more common as it remains released as long as the power is available. The: brake coil however has to be energized all the time and requires definite electrical interlocking with the main control so that the control is kept ineffective unless the brake is first energized. This creates a good deal of trouble in practice.

The present day general trend is to use hydraulic or electro-hydraulic' brakes. These brakes have proved effective, but largely depend on the proper functioning of the mechanism free from air pockets, and require definitely increased and more intelligent and careful maintenance In my invention, a scheme of control is devised, which stabilises the maximum light load speed of the motor, without reducing the set full load speed, and simultaneously allows the use of the simple and well tried out series-type electromechanical brake for emergency braking and holding of the motion.

The invention is fully described with reference to the attached drawing as follows:

(a) A circuit parallel to the motor armature A is added, controlled over normally open contacts of an electro-magnetic con-tact'or denoted as TF and called in this art as teaser field contactor, in series with which. a resistor R5 is so connected that when the contactor TF' is energized, the series field SF of the motor gets a direct circuit to the line Ll in parallel with the armature.

(b) The value of the resistor R5 can be selected so that the current passing independently through. the series field SF over the parallel path, called the teaser field path, is limited to a fixed value which gives a fixed limiting speed to the motor. It is proposed to set the resistance value R5 to such an extent, that the maximum steady light hook speed of the motor is limited to 125% of its full load speed.

(c) The operating coil TFI of the contactor TF is connected to the finger b of the master switch. The contact segment bl of the master switch engages the finger b in the off position of the handle as well as in position I in both the forward and the reverse directions. In other positions from 2 to 5 the segment is disengaged from the finger. Simultaneously, the coil TFI is connected over normally open contacts cemfa of the relay called counter-electromotive-iorce relay, the coil cemfl of which is connected across the terminals of the armature A. To make the circuit of the coil TFl complete, the negative line is taken over the second set of contacts cam b of the relay, in series with the normally open auxiliary contacts TFa. of the TF contactor itself; the negative terminal of the coil TB! is also taken over the normally open contacts 3ARa of the accelerating time relay 3AR.

(d) The relay with coil cemfl which is connected across the armature terminals is set to pull its plunger in, closing its two sets of contacts cemfa and cemfb, when the motor armature voltage reaches a fixed set value.

(6) Operation of the control system: To move the load from one position to another, the operator moves the master switch handle to position 5 in forward direction. The motor starts speeding up in sequence as the contactors IF, 2F, P, IA and 2A are energized one after the other. When the contactor 2A is pulled in, the relay coil 3AR! is shorted and the relay begins to time out. With the closing of the 2A contacts, the resistors Rl R2 and R3 are all shorted, and the motor has only the resistor R4 in the line. As soon as the resistor step R3 gets shorted, the motor armature begins to accelerate faster, the rate of acceleration depending on the load on the crane hook. The rate of acceleration depends on the rate of change of armature back-electro-motive force. If the relay with coil cemfl pulls in earlier than the timing of the relay with coil 3ARI, the coil TFI gets energized over the contacts cemfa and the contacts 3ARa both of which are closed at the same time. The contactor TF is therefore pulled in and the teaser field circuit is completed. The adiustments of the relay with coil cemf and the relay with coil 3ARI are so set that with one-third full load on the hook, relay with coil 3AR! times out before relay with coil cemfl relay can pull in. Therefore, for all loads less than one-third full load, the teaser field circuit is completed, whereas for loads one-third and above, the control works as a normal series motor control. If the crane driver wants that the crane bridge should coast a short distance, it brings the master switch in the off position, when the contactors IF and 2F have dropped down, disconnecting the motor armature from the power line. However, the coil TF1 of the contactor TF remains energized over the master switch finger b which engages with the segment bl, which keeps the teaser field circuit energized. The series field of the motor remains energized along with the series bra e coil. thus allowing the brake to remain lifted and the crane to coast. Referring to the drawing, it will be observed that on the first point of the master switch, the coil TFl gets connected to the positive power line over the master switch finger b. The connection is traced from the positive pole Ll of the control switch, over the fuse to the finger a of the master switch, then over the inter-connecting wire to the contacts Ma of the main contactor M. As the contactor M is energized, Ma contacts are closed, which gives the connection to the finger c of the master switch. As the finger 0 makes a constant contact with its segment cl, the continuity of the circuit is maintained over the interconnecting bar between segments cl and bl to the finger b of the master switch because in position l of the master switch, segment bl contacts finger b. Finger b is connected to one of the terminals of the coil TFl. Thus in the position I of the master switch, either in forward or reverse direction, the coil TFI always gets connected to the positive line. The other terminal of the coil TFl is connected to the contacts 3ARa of the relay 3AR, the connecting wire being taken over one common terminal of the contacts cemfb of the cemf relay. If, therefore, the contacts 3ARa also remain closed, the coil TFl will be energized in the position I of the master switch, as it will be connected also to the negative power line over the closed contacts 3ARa. The relay 3AR is energized by the voltage drop across the resistances (Rl+R2+R3) being connected to points TI and T4 of resistance R. With full load on the crane, when the master switch is brought from position 5 to position 4, 3, 2, and l in sequence, the motor resistances are re-introduced into the motor circuit by dropping out of contactors 2A, IA and P. The voltage drop due to the current through resistance R is such that the relay 3AR will pick up and close its contacts 3ARa before the master switch comes to position I. The coil TFl is thus energized as soon as the master switch is on position I. Once the coil TB! is energized and contacts TF close, the relay 3AR is kept energized, as the current will now branch off over the armature parallel circuit over the contacts TF, so that the voltage for the relay 3AR is maintained to keep its contacts 3ARa closed. When the master switch is brought to 01f position, the coil TFI, once energized on psition l. remains still connected to the power line as the circuit continuity is maintained even in the 01f position of the master switch. The electro-mechanical brake thus gets its holding power over the circuit given by the closing of the contacts TF. Therefore, whatever the load on the crane hook, the contactor TF gets energized as soon as the master switch is brought to position I, and remains so even in the off position of the master switch. The brake thus remains lifted and permits coasting of the bridge under all conditions. If the crane driver wants to stop the crane hv pl g ing, he reverses the master switch handle, which applies the plugging operation as already explained above. If the crane driver wants to plug the crane from the position 3 of the master switch, in that case too, as soon as the master switch passes over position l the TF contactor pulls in, because the relay with coil SARI remains energized completing the energizing circuit of the coil TFl. The series brake thus remains energized during the changeover to plugging operating. The controller therefore works as if the series brake is not provided. Only when the bridge is at standstill or when the power fails, does the brake drop down to hold the motion. The control system thus prevents overspeeding of the crane bridge when running with light loads and permits the use of a simple series type electromechanical brake to arrest the motion in case of an emergency, or to keep the brakes applied when the crane is at a standstill.

Having now particularly described and ascertained the nature of my invention .and the manner in which the same is to be performed, I de- .clare that what I claim is:

rent limiting resistor controlled by an electro- 1 magnetic contactor and connected in parallel circuit connection with the armature winding, herein called the teaser field circuit, the said voltage responsive means and the said fixed timedelay operating means in combination controlling the said motor speed control means, strengthening the motor field by diverting a fixed value of current through the motor field winding holding speed of the motor to a fixed maximum value, the said speed control means being connected in the circuit only when the motor speed exceeds a fixed value within a fixed time interval.

2. An electro-magnetic controller especially for a long travel mechanism of an electric travelling crane employing an electric circuit combining a direct current series wound motor, a source of energy and a manually operable master switch for starting, plugging and reversing the motor, having voltage responsive means, an electro-magnetic relay responsive to voltage across the motor armature, and time-delay responsive means, an electro-magnetic time-delay relay set for a fixed time interval, and motor speed control means, a current limit resistor controlled by an electro-magnetic contactor connected in parallel circuit connection with the motor armature winding, herein called the teaser field circuit, the said motor speed control means being controlled by the said voltage responsive means, responsive to the electro-motive force across the motor armature and the said timedelay means comprising the said electro-magnctic time-delay relay responsive to the voltage drop across a current limit resistor in the motor field circuit, the said voltage responsive means in combination with the said time-delay operating means controlling the said speed control I means, connecting the said teaser field circuit in parallel circuit connection with the motor armature, diverting a fixed value of current through the motor field winding, so strengthening the motor field holding the motor speed to a fixed maximum value.

3. An electro-magnetic controller especially for a long travel mechanism of anelectric travelling crane employing an electric circuit combining a direct current series wound motor, a source of energy and a manually operable master switch for starting, plugging and reversing the motor, having voltage responsive means, an electro-magnetic relay responsive to voltage across the motor armature, and time-delay responsive means, an electro-magnetic time-delay relay set for a fixed interval, and motor speed control means, a current limit resistor controlled by an electro-magnetic contactor connected in parallel circuit connection with the motor armature winding, herein called the teaser field circuit, and an electro-mechanical braking means, an electro-mechanical brake mounted on the motor shaft, its energising coil being connected in series connection with the motor armature winding and the motor field winding, the said motor speed control means being controlled by the said voltage responsive means responsive to the electro-motive force across the motor armature and the said time-delay means comprising the said electro-magnetic time-delay relay responsive to the voltage drop across a current limit resistor in the motor field circuit, the said voltage responsive means in combination with the said time-delay operating means, controlling the said speed control means, connecting the said teaser field circuit in parallel connection with the motor armature, diverting current through the motor field Winding and through the energizing coil of the said electro-mechanical braking means in series connection with the motor field winding, the current through the operating coil of the electro-mechanical braking means, maintaining the energizing power and restraining the application of the electro-mechanical brake despite the reversible movements of the said manually operable master switch required to manipulate the direction of motion of the long travel mechanism. of the crane.

.KAIKOBAD S. KUKA.

REFERENCES CITED The follow-ing references are of record in the file of this patent:-

UNITED STATES PATENTS Number Name Date 653,471. Cutler July 10, 1900 710,581 Ihlder .Oct. '7, 1992 743,463 Cutler Nov. 10, 1903 1,062,096 Henderson i May 20, 1913 1,605,977 Oswald i Nov. 9, 1926 2,455,226 Harris Mar. 22, 1949 

